1. Field of the Invention
The invention relates to a method and apparatus for expanding foodstuffs and luxury foodstuffs/tobacco materials. In particular, the method and apparatus in accordance with the invention may serve to increase the filling capacity of tobacco material or smoking materials reduced in size.
Concerning tobacco material, what should be understood as being included under the term tobacco material or smoking materials reduced in size are threshed tobacco leaves, tobacco stems, tobacco stalks, each cut or shredded, reprocessed tobacco as well as by-products of tobacco such as winnowings in tobacco processing (primary) and in cigarette production and packaging (secondary).
2. Description of Prior Art
Freshly harvested green leaves of tobacco contain a relatively high proportion of water, the residual content of which is reduced by means of various curing methods to less than 10% by mass. The water content is defined as the loss in mass of the tobacco relative to a moisture weigh-in in % by mass in a drying cabinet in a drying time of 3 hours at 80xc2x0 C. (so-called Salvis moisture). Tobacco prepared as such constitutes raw materials, termed raw tobacco, employed in making e.g. cigarettes or other tobacco-based luxury foodstuffs. The processing chain involved from green leaf up to raw tobacco results in heavy shrinkage, this reduction in volume has a disadvantageous effect on the so-called filling capacity.
The tobacco industry describes filling capacity as the ability to produce finished products (e.g. cigarettes) using as little mass as possible, yet, which are physically stable, firm or hard. (filling capacity also is defined as the remaining volume relative to the weigh-in in ml/g which is derived from compression with a 3 kg weight in a cylindrical vessel after time available of 30 seconds).
Physical and chemical procedural principles are known technically for reversing the shrinking process:
The physical procedures (gaseous change in phase by heat supply) differ substantially by the impregnation means/expanding agent and thus by the change in phase, examples of which are impregnation with CO2 (solid to gaseous change in phase), impregnation with liquid gas (liquid to gaseous change in phase) as well as impregnation with high-pressure N2 (dissolved to gaseous change in phase).
Also to be mentioned in this respect are the methods proposed with organic solvents in liquid form and expulsion as gas, this describing substantially all known low-boiling methods.
The variants of the chemical procedures (generating a gas by thermal decomposition or exothermic reaction) differ substantially by the way the gas reacts in being generated, such as decomposing additives by introducing heat in the dryer or by the addition of further additives to trigger a reaction. Examples of this are impregnating with NH3/CO2 (solid to gaseous thermal decomposition) with H2O2 (liquid to gaseous thermal decomposition) and with N2H4/H2O2 (liquid to gaseous exothermic reaction).
Only the physical methods have succeeded in gaining cost-effective significance, typical of which is pressurized impregnation. Subsequent expansion in the dryer is done after the so-called fixing instigated by reducing the pressure/cooling to atmospheric pressure in the impregnator to thus create an equilibrium substance at atmospheric pressure. The significance of these processes is explained by expansion being free of residues, low-cost expanding agents and an increase in volume in the order of magnitude around factor 2.
The drawback with these methods is the need to infeed extra additives and the necessity of a pressurized stage in the tobacco treatment process, impregnation normally being a complicated batch process.
The chemical procedures have gained no significance whatsoever due to the residue problems involved. In all known methods, the tobacco is impregnated either at or above atmospheric pressure with substances which, in a second step, e.g. in a dryer, are quickly put through a change in phase from solid or liquid state into a gaseous phase. This bloating effect results in the increase in volume of the tobacco structures. Known from DE 31 47 846 C2 is a method of enhancing the filling capacity in which the tobacco material is introduced into a carrier flow in a venturi nozzle, it thereby expanding. The drawback in this arrangement in the need to optimize the increase in filling capacity.
As regards the expansion of other foodstuffs and luxury foodstuffs/tobacco materials/tobacco materials capable of expansion (e.g. cereals or pulses; xe2x80x9cpuffsxe2x80x9d), prior art mostly describes discontinuous methods and apparatuses; the following prior publications to be cited in this respect:
DE 195 21 243 describes a method and apparatus, wherein in batch operation a closed vessel is pressurized and the material contained therein heated. The upper portion containing no material is briefly exposed to increased pressure. By the vessel being abruptly opened, the material is output into an expansion chamber at atmospheric pressure. The increased pressure acts as an expansion agent, resulting in the water contained in the material being evaporated and causing said material to expand.
DE 195 21168 describes an apparatus and method analogous to those of DE 195 21 243 except that, in this case, the inner vessel features no holes in the upper portion containing no material.
DE 195 21167 describes an apparatus similar to that of DE 195 21 243 and DE 195 21 168, except that, in this case, the expansion chamber is rotatable and the expanded material is discharged longitudinally by rotation of the drum.
DE 198 06 951 describes an apparatus and a method for buffing a granular material, more particularly a preheat chamber for the material to be expanded. The heater employed comprises a fluidized bed chamber, in which the material is heated batchwise. With the aid of a branch circuit, the product is transferred to the buffing reactor.
Described in DE 198 06 950 is an expansion chamber configured two-part. The first part begins directly at the discharge of the expansion chamber and has the configuration of an elongated slim cone, designed to result in a laminar flow. It ports into the second part in which normal pressure is attained at the latest. Here the flow is turbulent.
Also in the case of this prior art, expansion can still not optimally occur and the systems operating in discontinuous batch operation are complicated and not very effective.
The object of the present invention is to overcome the aforementioned disadvantages of prior art, the intention being more particularly to effectively make optimum expansion possible and, as regards the tobacco material, it is intended that the cited reduction in the filling capacity/shrinkage is to be counteracted as much as possible.
This object is achieved in accordance with the invention by the subject matter of the independent claims. Preferred embodiments of the invention read from the sub-claims.
The invention makes it possible to attain, in the field of tobacco processing, increases in the filling capacity, not achievable up until now, and which, after expansion, are as much as 10 percent above the values for usual methods of expansion hitherto generally deemed optimized. The positive effects on the cost-effectiveness in producing smoking products are enormous in view of the amounts of tobacco material used in the industry. Corresponding benefits materialize in the area of other expandable foodstuffs and luxury foodstuffs/tobacco materials.
In the method in accordance with the invention the material continuously passes through a zone of elevated pressure, followed by a zone of reduced pressure before ending up in a zone of atmospheric pressure.
The core principle of the method exploits the ability of gases and vapors to totally convert compression energy by means of a nozzle into kinetic energy (in the extreme case, reducing pressure down to 0 bar). This extreme reduction in pressure can only be achieved when at the narrowest location of the nozzle the speed of sound or equivalently the critical pressure ratio is attained. Under these conditions, a further reduction in pressure and thus increase in velocity occurs in the wider section of the nozzle.
Under the same conditions in classic operation of such a nozzle an increase in pressure and thus reduction in volume occurs in the wider section, as is evident from the enclosed FIG. 6 showing, in the upper illustration, a basic nozzle construction, the velocity and pressure profiles for various modes of operation being illustrated below. In this arrangement, the profile identified by the encircled 1 applies to a nozzle in critical closing operation, while the profiles identified by the encircled 2 are for a Laval nozzle in critical operation (at supersonic speed) as used in the present invention.
When a carrier flow (for example saturated steam) is charged e.g. with tobacco material prior to it entering the nozzle, then depending on the input conditions the particles are equilibrated to the temperature and pressure of steam (e.g. 4 bar, 143xc2x0 C.). Once the two-phase mixture has entered the vacuum zone of the Laval nozzle (e.g. 0.2 bar) the moist particles lose their equilibrium at an elevated temperature (boiling point of water at 0.2 bar: 60xc2x0 C.) and tobacco moisture evaporates for cooling. This forced evaporation is fed from the internal particle energy. Any transfer of heat from the surroundings is impossible due to the temperature conditions (vapor colder than particles) in the vacuum zone. However, heat is transported outside from inside by the conduction of heat in the particles. Dehumidification/drying in this way is basically different to the so-called convection air-flow dryer, in which the energy required for evaporation is transferred from the gas to the particles.
Due to the very low pressure at the exit of the Laval nozzle, the increases in the filling capacity can be advantageously achieved. In addition to this, the invention makes a continual process possible which can be integrated e.g. in a tobacco preparation process without any special steps being needed (it permitting more particularly integration in an air-flow dryer without first needing to outfeed the tobacco). Thus, this arrangement involves only a minor additional apparatus; additional steps in preparing the tobacco such as casing or flavoring can be directly integrated.
The carrier flow may comprise a steam content of 10 to 100% saturated steam and, more particularly, comprises superheated steam.
In one embodiment of the invention, the pressure of the carrier flow upstream of the Laval nozzle is in the range of less than 1 bar to approx. 30 bar, preferably 1 bar to 30 bar and more particularly 1 bar to 10 bar, and the temperature of the carrier flow upstream of the Laval nozzle is in the range of 50xc2x0 C. to 450xc2x0 C., preferably in a range of 100xc2x0 C. to 300xc2x0 C.
The pressure at the output of the Laval nozzle may be in the range of 0 to 2 bar, preferably 0.2 to 1 bar.
Described more particularly in the following are embodiments for expanding tobacco material. However, these embodiments are just as suitable for expanding is other foodstuffs and luxury foodstuffs/tobacco materials, including processing solid, fibrous, grainy, bean or leafy foodstuffs and luxury foodstuffs/tobacco materials, e.g. grains, pulses, cereals, barley, maize, beans, wheat, rice or peas. The components of the apparatus, such as separators, are then to be adapted to the material to be processed in each case.
Preferably, the carrier flow is superheated prior to the material/tobacco material being incorporated.
In one preferred embodiment of the method in accordance with the invention, the carrier flow passes through an infeed zone, a nozzle antechamber, the Laval nozzle, an infeed diffusor and an outfeed diffusor.
On the one hand, the tobacco material may be fed into the carrier flow in the infeed zone upstream of the Laval nozzle, preferably via a rotary vane lock comprising a header placed onto the infeed zone.
On the other hand, it is possible to feed the tobacco material into the carrier flow at the Laval nozzle in the zone of lowest pressure, preferably via a rotary vane lock comprising a header placed onto the Laval nozzle.
As far as further processing of the tobacco material is concerned it is possible in accordance with the invention to supply the tobacco material, after it having passed through the outfeed diffusor, to a tobacco separator, more particularly a centrifugal separator, the vacuum of which is maintained preferably by a vacuum compressor. However, after it having passed through the outfeed diffusor, the tobacco material may also be first supplied to an air-flow dryer and then to a tobacco separator, more particularly a centrifugal separator.
In one advantageous embodiment of the method in accordance with the invention, the gas flow passing the components adjoining the outfeed diffusor is collected by means of an air recycling system, compressed and recycled as part of the carrier flow.
The apparatus in accordance with the invention is preferably characterized by it comprising a means, more particularly a heat exchanger, for superheating the carrier flow prior to the tobacco material being incorporated.
In one development of the apparatus in accordance with the invention, the flow guidance means comprise an infeed zone, a nozzle antechamber, the Laval nozzle, an infeed diffusor and an outfeed diffusor.
A rotary vane lock having a header placed onto the infeed zone may be provided, by means of which the tobacco material is fed into the carrier flow in the infeed zone upstream of the Laval nozzle.
Furthermore, the apparatus may comprise a rotary vane lock having a header is placed onto the Laval nozzle, by means of which the tobacco material is supplied to the carrier flow at the Laval nozzle in the zone of lowest pressure.
Preferably, the apparatus comprises a tobacco separator, more particularly a centrifugal separator to which the tobacco material is supplied after having passed through the outfeed diffusor, and the vacuum of which is maintained preferably by means of a vacuum compressor.
In another embodiment, the apparatus comprises an air flow dryer and adjoining thereto a tobacco separator, more particularly a centrifugal separator, to which the tobacco material is supplied after having passed through the outfeed diffusor.
It is particularly advantageous to provide an air recycling system by means of which the gas flow passing the components adjoining the outfeed diffusor is collected, compressed and re-supplied to the carrier flow.